1. Technical Field
This disclosure relates to modular metering devices, and more particularly, to a group metering device with individually field rephaseable meter sockets to selectively balance tenant loads on at least three phases.
2. Description of the Related Art
Utility companies transfer electrical power in three phases (A, B, and C phase) of alternating current (AC) power which are synchronized and offset from each other by 120 degrees. The three phase power is transferred over three wire lines, in addition to a ground or neutral wire, to transformers, which converts the power to lower distribution voltages. A main service panel then distributes single phase electrical power (AB, BC, or AC) to each tenant or customer.
The voltage between the two phases of each single phase of electrical power is typically 240 volts of alternating current (VAC) in the United States, and the voltage between each phase to neutral is 120 VAC. 120 VAC electrical power provides electricity for such uses as lighting, while 240 VAC electrical power is adaptable for major indoor appliances, such as air conditioners, water heaters, stoves and ovens, etc., as well as for outdoor power uses such as motors for swimming pools, jet tubs, fountains, etc. All currents are returned to the electrical circuit after tenant consumption through neutrals.
In most circumstances, neutrals are jointed together and grounded at the customer main service panel or at the transformer. Therefore, it is important that the tenant loads be balanced to use electricity efficiently as well as to prevent overload to any electrical phase that may cause overheating of conductors.
In high-rise buildings, apartments, and some office complexes, utility companies may provide three phase electrical power through bus ways or cables to a service entrance which is connected to modular meter stacks (group metering) to distribute three phase electrical power to single phase meter sockets, and ultimately to the tenant. Due to the similarity of any individual unit, each unit typically requires almost same tenant load for each meter position/tenant. Therefore, by having an equal number of meter positions/tenants on each of the single phase combinations (AB, BC, or AC) the total load can be balanced over all three phases.
Starting in 1970's, meter socket stacks offered 2 to 6 meter position devices with three phase through buses but single phase interior riser bus. Such meter stack devices could not be rephased after factory installation. Contractors had to predetermine a calculated tenant load and then buy pre-phased different meter position meter stacks to achieve an equal number of meter positions on any single phase. This required a very complex calculation and ordering process in order to achieve a balanced phase combination, including taking into consideration such issues as the number of meter positions required, each phase tenant load, the existing product selection, and lead time.
In the late 1990's, field phase changeable meter stacks were invented that allowed reconnection of single phase riser buses to different phases after factory installation. This was quite advantageous compared to the earlier non-rephaseable meter stack devices. For example, if four meter position units were needed, contractors had to order each of separate pre-phased AB, BC, and AC units in the non-rephaseable version. With the field rephaseable device, contractors only needed to order three same units and convert them to AB, EC, and AC phasing as needed in the field.
U.S. Pat. No. 5,936,834 to Polston et al. (hereinafter Polston) discloses a meter stack wherein each single phase meter base in the meter stack can be selectively connected in the field to any one of the three phase combinations by moving meter base line connectors. The meter stack allowed contractors to change the phase combination on any individual meter socket. Polston's device addressed situations wherein the number of tenants was not a multiple of three or where significant changes were needed for rebalancing the tenant load after calibrating the circuit. It was desirable to alter a few meter sockets to different phases on the job site.
Accordingly, an efficient and effective device and method for enabling field rephrasing of individual meter sockets in a modular metering device, is highly desirable.